You asked!
I consider myself well versed in the SE/DE comparison and there are several conversations to be had here.
· PAR output
· Shielding
· Spectral output
· Reflector/Bulb distribution
· 250W DE, 400W DE
· Bulb selection/replacement cost
PAR:
Comparing the PAR variance on bulbs made by the same manufacturers isn't the way to go. Some bulb makers are simply better at making DE bulbs while others are better at making SE bulbs.
Example: The 250W Iwasaki 6500K SE bulb yields 189 PPFD while the unshielded 250W EVC 10K DE yields 179 PPFD. Such a slight drop in PAR while significantly “whitening†the spectrum is very good.
So what about shielding(s)?
MH bulbs emit toxic levels of UV A, B, and C. In order to protect people/animals from harmful UV a glass shield is used. SE bulbs are made with a safely rated shield. DE bulbs require an external shield (usually mounted below the bulb).
Most DE pendant makers use low grade E-glass as a shield. It is a green glass with reflective qualities, so while effective at shielding UV it also reflects a portion of the otherwise useable light back up toward the bulb. It seems the consensus of PAR degradation is between 10 and 20%. This can be greatly improved by using an aftermarket glass replacement from a framing or glass shop. Tru-view museum grade glass was my choice. It is a low iron glass like Starphire with antireflective qualities. You need to be careful about the cheaper anti reflective glass because they achieve reducing reflection by etching. This will reduce the light making it through the glass so stick with the good stuff. My Tru-view glass shield for a Luminarc3 ran be about 15.00.
While PAR and the impacts shielding has on it is important, in the bigger picture PAR is a small portion of you lighting decision. Virtually all aquarium MH bulbs can sustain and grow high light demanding photosynthetic life.
Spectral output:
Spectral output determines and impacts a number of things. It changes the appearance of the tank to the human eye. It encourages/influences coral pigment coloration. It also impacts the intensity of the useable light (PAR).
Spectrum is measured in Kelvins (K). The lower the Kelvin the yellower the appearance of light. I won’t dive into the heart of spectrum but I will keep it simple and relevant to the SE/DE comparison.
SE and DE bulbs regardless of assigned Kelvin (10K, 14K, 20K…) emit different spectral outputs. So a 14K DE bulb may look perfect to you while the SE counterpart doesn’t. In my case the 400W DE 20K looked great to me while striking a balance of color and PAR. Radium being on the Blue end and 10K XM’s being too yellow the PFO 400W DE was juuust right
Reflector Distribution:
Light emitted off the bulb is one thing but what makes it into the tank is entirely different. The reflector used determines where the light will we distributed and how.
SE bulbs can be housed in a number of reflectors. Pendants, Spider-type Parabolic, Luminarc3, even aluminum gutters! While in theory this can also be said about DE bulbs, retrofitting will be necessary in all cases except the pendants. Pendants are an area where DE bulbs shine (pun intended). The shape of the bulb married to a parabolic pendant reflector creates a very efficient emission of light. This is good and bad, because while showing peak PAR that is through the roof near the center of the reflector, the outer areas drop.
IMO the pendants are good for smaller tank applications with special constraints. As soon as your tank gets wider than 18-24†you might begin wishing you had a more even distribution across a square shaped area versus a laser beam up the middle in a rectangular shape.
I myself retro-fitted an Luminarc3 to support a 400W DE bulb and IMO this was a very successful implementation. Good color/PAR balance with a wide 24-30†square distribution that was pleasing to my eyes.
A real quick note on bulb distribution: SE and DE bulbs are different in size and shape. This also impacts the light distribution. The 400W DE bulb is very long and in my experience achieves better intensity coverage, but at the same time with L3 reflectors this virtually becomes a mute point because the L3 is so good at evening out the entire distribution.
250W DE, 400W DE:
By far and large the 250W DE bulbs are much more prevalent in the hobby. The 400’s are fairly new, very expensive, and other little motivation to change from SE, unless you have my eyes
I have been impressed however with how closely the DE’s PAR performs even with a glass shield. I observed obvious faster growth with the 400DE 20K versus the 400W 20K Radium I was running in tandem.
Bulb selection/replacement cost:
The 250W DE offer a large selection at SE prices. Some of the DE bulbs are very efficient and have attractive spectral outputs. The 400’s are stupid expensive ranging from 90.00 per bulb to 120.00!!! ::cough cough:: Although the prices will likely fall if 400’s continue to sell and new 400 bulbs are made, but as it stands the selection is very limited if not difficult to find.
SE bulbs are EVERYWHERE in EVER form at EVERY price ranging from 40.00 to 150.00.
I have not identified a significant difference in the lifespan of SE vs DE bulbs
So in summary the SE bulbs IMO are appealing to a far larger audience than DE bulbs.
I hope this helps... There is plenty i didn't bring up or explaing in detail but I'll be around
